LT1500 Mower--New Carburetor- Surging at Full Throttle

[MM85]

Hello,

I have read many forums and they've told me everything I've already tried. Maybe someone else has an idea. I have a Craftsman LT1500- 17.5 HP Briggs&Stratton Silver Edition Engine. It's a 2012 model. (Model#: 247.288812)
(Serial#: 1B202B30416) (Engine model#: 31C707) (Engine Type: 3346 G6)

The main issue I'm having is that the mower surges at high idle. I bought a new carburetor, replaced the gaskets, new gas, new filter (and ran it without a filter), have cleaned the new carb multiple times, made the spring tighter on the governor to see if it was worn out, adjusted the governor and idle screws every which way, I've put the cover over where the air filter goes too. This happens with the old carb and the new carb. It idles good, runs good on high idle for about 5 seconds. After 5 seconds it starts to surge at high idle or under a load. You put it back down to idle for a few seconds, rev it back up to full throttle, it does good for another 5 seconds, or so, and then it'll surge again. When it surges and you spray carburetor cleaner in the intake it'll run perfect on high idle until it burns off all the carb cleaner. I can make it run perfect without any hesitation or surging if I remove the filter, place my hand in a cone shape over the hold where the filter sits and restrict the air flow. As long as I keep my hand there, the mower runs perfect at any throttle position. I bought an LT2000 and it started doing the same thing.

 

[Romore]

Hold your finger on the throttle, if it smooths out the governor is set incorrectly. If it stumbles and dies it is not getting enough fuel. It may be over revving which will starve it for fuel.

 

[bertsmobile1]

did any one suggest cleaning out the fuel tank ?
Did you try spraying WD 40 or similar from a trigger pack all over the carb & intake manifold to check for induction leaks ?
On a governed engine surging is always caused by too little fuel and the governor over correcting.
That leaves two possibilities.
Not enough fuel getting into the carb
or
Air entering after the fuel has been mixed with the incoming

 

[MM85]

I've cleaned the tank and sprayed starting/carb cleaner over all the ports where air would come in, along with all over the carb, and there is no change in rpm; it still fluctuates. I cannot hold the governor still. It never dies when I hold down the throttle. I take off the carb and there is plenty of fuel in bowl every time. I take it off when it is surging to see and the bowl is always plentiful. When the foam piece to the governor shaft is sprayed with carb/starting fluid it will jump in rpm and level out/run smooth on high idle.

 

[bertsmobile1]

Please be careful what you type.
Remember we have nothing to go on but what you have written on the screen.
The governor shaft comes out of the engine .
It has the governor arm clamped to it
The other end has he throttle rod
It connects to the throttle butterfly
the throttle butterfly is mounted on a shaft that goes through the carburettor.
The top of this shaft has a foam ring on it to prevent dirt getting in.
If that shaft has any movement other than rotating then the carburettor body has worn out
Is this where you were spraying the carb cleaner that caused the engine to speed up ?

In the bottom of the carburettor is a fuel shut off solenoid.
From what you have typed I think the solenoid is not staying fully open & restricting the fuel flow .